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Full text of "The Morphology And Evolution Of The Apes And Man"

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18           MOKPHOLOGT AND EVOLUTION
i
occipital plane is perpendicular to the basicranial axis, and two globular swellings—the tympanic bullse— project downwards from the basal aspect of the temporal bones, A great difference, however, will be seen in the orbito-ternporal region: in the Dog the orbital cavity is not shut off in any way from the temporal fossa, but a post-orbital bar, formed by the frontal and malar bones, partially separates them in the Lemur. Within the orbit in the Lemur the ethmoid and lachrymal bones are separated by a union of the frontal and maxillary bones. Xo trace of the nasal duct appears within the orbit, but the orifice is seen on the face.
On the side of the skull the most important point to note is the union of the parietal and alisphenoid bones in the pterion.
The glenoid cavity for the reception of the condyle of the mandible is extremely shallow, but there is a well-marked post-glenoid tubercle. The jugular foramen is large, and the internal carotid artery passes into the skull through a foramen on the back of the tympanic bulla.
The external auditory meatus is shallow, whereas it is long in the Anthropoid Apes.
The foramen rotnndum and spheno-maxillary fissure are confluent, and there is no canal in the alisphenoid for the internal maxillary artery as there is in the Dog. The bony palate is long, and may be thickened behind. The turbinal region is complex; and the condyles of the mandible are level with the crowns of the molar teeth.
The dental formula is If C* PM| M| in the true
*r
Lemurs.   In the Indrisidae it is reduced to If OJ PM|